1. Field of the Invention
This invention relates generally to the clamping of elastomeric hose and tubing to fixtures and hose coupling devices and to the use of bands of heat shrinkable polymer to provide a constrictive force about elastomeric hose and tubing. More particularly, this invention relates to an improved elastomeric hose and tubing clamp formed of a band of heat shrinkable polymer. Specifically, this invention relates to an improved clamp for sealing hose and tubing to fixtures and couplings associated with automotive coolant systems.
2. Description of the Prior Art
Elastomeric hose (reinforced) and tubing, hereinafter generically referred to as hose, are commonly used to convey various fluids where those fluids are under a variety of pressures and temperatures, as part of fluid transport systems. For these systems to be operable, the connections between hoses and the items with which the hoses fluidically communicate must be fluid tight and able to resist separation that would otherwise occur because of influence from the fluid pressure, or blow-off, as well as surrounding environment, or pull-off.
Commonly, these connections are made by placing the open end of the hose over a stem or coupling insert. The hose and the associated stem or insert are ordinarily sized and shaped to allow the open end of the hose to slip over the stem or insert and to seat with a snug fit. For systems operating at certain pressures and in certain environments, nothing more is required. More typically, however, a hose clamp is installed near the open end of the hose, urging the hose more tightly upon the stem or insert to resist leakage, blow-off, and pull-off.
Hose clamps have been produced in various sizes, shapes, and materials. One common style of hose clamp, the adjustable threaded strap clamp, has included a metal strap with a housing affixed to one end, the housing end. The housing has a space that allows the opposite end of the strap, the free end, to be inserted therethrough such that the strap folds back upon itself to form a band. The housing also contains a threaded screw mechanism. The strap, starting at the opposite end, has a series of indentations or slots that are adapted to mate with the threads of the screw mechanism. In practice this style of hose clamp is wrapped around the hose at the location where clamping is to occur; the free end is inserted into the space of the housing to where the threads and indentations or slots engage; then the screw mechanism is rotated to tighten the clamp.
This style of hose clamp is simple in construction and can produce relatively substantial dynamic and static hoop stresses. Dynamic hoop stress is the constrictive force the clamp exerts upon the clamped object as a result of the inner diameter of the clamp being actively reduced, in this case, by the action of the screw mechanism. The static hoop stress is the constrictive force the clamp exerts upon the clamped object when countering an expansion force being exerted upon the clamp by an active expansive attempt by the clamped object. Depending upon the hose clamp construction at issue, these two stresses can be the same or different. The threaded strap clamp can be expected to produce different dynamic and static hoop stresses. The dynamic hoop stress is expected to be limited by the force the screw mechanism can produce. The static hoop stress is expected to be limited by the point at which the screw becomes disengaged from the indentations or slots.
The threaded strap clamp's relatively substantial hoop stresses produce a connection with a high resistance to blow-off and pull-off. However, the threaded strap clamp suffers from numerous disadvantages. As it is constructed from a strap, it has two relatively sharp edges that ring the connection end of the hose, providing an opportunity for hose damage and failure. Depending upon the metal from which it is formed, it can also be susceptible to corrosion. The screw housing and mechanism protrude from the strap taking up sometimes valuable space and providing a place for objects of the environment to become entangled. The nature of the screw mechanism requires a tool for operation and sometimes valuable free space from which to operate the tool. The clamp is not readily susceptible to automated assembly line installation and is relatively time consuming to install by any method.
The threaded strap clamp's most significant disadvantage, at least in automotive coolant system applications, is its inability to resist cold leaks over time. A cold leak occurs when the coolant system is cold and is the most prevalent and persistent type of leakage problem in modern automotive coolant systems. While old systems are more prone to exhibit such leaks, new systems are not immune to the problem. A common source for cold leakage is where the combination of elasticity and coefficient of thermal expansion of the clamp material is inadequate to follow the contraction of the material of the stem as both cool. After only a few heat cycles of the coolant system, the thermal expansion activity of the stem and clamp causes some of the material of the hose to flow from between the stem and the clamp. This leads to an effective loosening of the clamp. Then as the system cools, the stem shrinks away from the inner surface of the hose, and the seal is broken; the system fluid then leaks.
Cold leaks are also exacerbated when the hose clamp employed exerts non-uniform constrictive force about the circumference of the connection end of the hose. Such non-uniformity also leads to leaks at times other than when the system is cold. In either case, non-uniformity can allow a separation between the stem and the hose, breaking the seal and allowing a leak.
The threaded strap hose clamp also suffers from applying a non-uniform constrictive force, particularly where the housing joins the strap and at the point where the ends of the strap overlap due to both the geometry of the clamp and the relative rigidity of the material of the clamp. Non-uniformity of constrictive force is further increased when irregularity exists in the shape of either the hose or underlying stem, which this style of clamp cannot accommodate. However, the materials of the threaded strap hose clamp tend to be resistent to the chemicals found in the automotive coolant system environment.
Another common style of hose clamp is the screw clamp. This style of clamp is either formed into a band from a strap, as in the threaded strap clamp, or formed into two substantially parallel bands from heavy wire. Projecting radially and outwardly from and near the ends of the band or bands are two stand-offs. One of the stand-offs includes internal threads for receiving a screw; while the other includes a hole that is sized to allow passage of the shank of the screw but not the head. A screw extends between the stand-offs. When the screw is rotated, the clamp is tightened. The screw clamp has characteristics that are very comparable to those of the threaded strap clamp.
Yet another common style of hose clamp is the constant tension spring clamp. The spring clamp is formed of spring material into a band with overlapping ends. Commonly, one of the ends is forked to allow the overlapping to occur with one end interposed between the forks of the other end. An inverted "U" shaped projection extends radially from the forked end. An "I" shaped projection extends radially from the other end. Both projections are end portions of the band bent outwardly. When the two projections are squeezed toward each other, the inner diameter of the clamp increases. In practice, the clamp is held in this expanded position by a cap that is placed upon the two projections; the clamp is positioned over the connection end of the hose; the hose is placed upon the stem or insert; and the cap removed from the projections allowing the clamp to contract upon the hose, clamping the hose onto the stem or insert.
The spring clamp has advantages over the clamp styles previously discussed. It is very susceptible to rapid, modern assembly line installation. Moreover, it is more effective in mitigating cold leaks, if applied with great care. Its improved effectiveness against cold leaks emanates from the greater uniformity with which it constricts about the hose and the characteristic of self-adjustment. The self-adjusted characteristic stems from the spring nature of the clamp; as the hose and the stem change dimension as functions of time and temperature, the clamp correspondingly changes in dimension. There are, however, apparently some severe limitations on the amount of self-adjustment available as self-adjustment has ill effects upon the uniformity of constriction.
The spring clamp has continuously varying amounts of material in relation to angular position around the circumference of the clamp to compensate for a geometry that would otherwise produce significantly varying constrictive force about that circumference. This results in a substantially uniform constrictive force for a given design diameter assumed by the clamp in the presence of a hose. As time and temperature have their affects upon the hose and stem, for which the spring clamp is to adjust, the diameter that the clamp assumes changes. The greater the adjustment deviates from the given design diameter, the greater the non-uniformity of constrictive force. The net result is that a spring clamp is more resistent to cold leaks, but not impervious to them.
Further, the spring clamp projections, like the housing and mechanism of the threaded strap clamp, protrude from the clamp taking up sometimes valuable space and providing a place for objects of the environment to become entangled; and, the materials adaptable to this and all clamps previously discussed are relatively heavy.
All of the previously discussed clamps are necessarily made of materials incapable of accommodating irregularities in the hose and stem shapes.
U.S. Pat. No. 3,315,986, Quick, discloses a different approach to clamping elastomeric hose to a stem or insert. That disclosure indicates placing a heat-shrinkable synthetic resin tube about the elastomeric hose; placing the stem or insert within the connection end of the hose; placing a pyrotechnic material around the assembly; igniting the pyrotechnic material and thereby shrinking the synthetic resin tube and clamping the hose onto the stem or insert. That U.S. patent specifically discloses the use of heat-shrinkable polymerized chloroprene; heat-shrinkable tetrafluoroethylene, and heat-shrinkable polyorgano siloxane elastomers. According to '986, these materials are formed then mechanically expanded. This activity is sometimes referred to as orienting the polymer. The '986 patent specifies the oriented, or expanded, dimensions to be approximately 20 percent greater than the pre-oriented, or pre-expanded, dimensions.
The '986 patent provides as an exemplary application the repairing of a garden hose by use of the materials and method described above. The '986 patent apparently envisions an environment where dynamic and static hoop stresses that are relatively small will suffice, as indicated by the exemplary application offered and the materials specified. Further, the need for self-adjustment by any clamp used in automotive coolant systems, to eliminate cold leakage, was apparently not recognized or addressed. Also, resistance to chemicals commonly found in the automotive coolant system environment was not addressed.
The need remains, particularly in the automotive coolant system environment, for a hose and tubing clamp that; substantially eliminates cold leaks by being self-adjusting over a significant range of thermal and temporal conditions while concurrently providing uniform constrictive force; provides sufficient dynamic and static hoop stresses to resist blow-off and pull-off is capable of conforming to irregularities of hose and stem shapes commonly found in automotive coolant system applications; is adequately resistent to the chemicals of the automotive coolant system environment; is resistent to corrosion; is fast to install and susceptible to modern assembly line installation; is lightweight; and, is devoid of projections that waste space and can be a source for collection of debris.